1. Field of the Invention
The invention relates to a hybrid vehicle and a hybrid-vehicle control method.
2. Description of the Related Art
Japanese Patent Application Publication No. 2005-180255 (JP-A-2005-180255) described a hybrid vehicle having an engine, a motor-generator that generates electric power using the drive force of the engine and produces drive force to assist the engine, and a power storage device that powers and is powered by the motor generator. According to this publication, when the hybrid vehicle is running in an area where the density of air drawn into the engine is low, such as a high-altitude area, the target charge level of the power storage device is increased to prevent the charge level of the power storage device from becoming too low to compensate for a decrease in the engine output.
As such, in a hybrid vehicle, it is important to properly manage the charge level of the battery. In the case of a hybrid vehicle that runs by converting the drive force of an engine into torque via two electric motors and a planetary gear mechanism, when the hybrid vehicle is running in an area where the atmospheric pressure is low, such as a high-altitude area, the output of the engine decreases due to the low air density, and therefore the power discharge from the battery increases, resulting in an excessive decrease in the charge level of the battery.